Dynamic android picture gallery

I am learning Android, and I want to create simple application with few buttons on main page, each leading to small gallery. I created such application, but pictures are statically linked. What would be the best way to make it dynamically load  as much as pictures as there are in res/drawable folder ? I need simplest possible method for that. Here is my code:

GalerijaApartmani.java

package rs.limitline.topcider;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;

public class GalerijaApartmani extends Activity implements OnClickListener {

	private ImageView imageViewMain;
	private ImageView imageView1;
	private ImageView imageView2;
	private ImageView imageView3;
	private ImageView imageView4;
	private ImageView imageView5;
	private ImageView imageView6;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.galerija_apartmani);
		imageViewMain = (ImageView) findViewById(R.id.imageViewMain);
		imageView1 = (ImageView) findViewById(R.id.imageView1);
		imageView2 = (ImageView) findViewById(R.id.imageView2);
		imageView3 = (ImageView) findViewById(R.id.imageView3);
		imageView4 = (ImageView) findViewById(R.id.imageView4);
		imageView5 = (ImageView) findViewById(R.id.imageView5);
		imageView6 = (ImageView) findViewById(R.id.imageView6);
		imageView1.setOnClickListener(this);
		imageView2.setOnClickListener(this);
		imageView3.setOnClickListener(this);
		imageView4.setOnClickListener(this);
		imageView5.setOnClickListener(this);
		imageView6.setOnClickListener(this);
	}

	@Override
	public void onClick(View v) {
		ImageView imageView = (ImageView) findViewById(v.getId());
		imageViewMain.setImageDrawable(imageView.getDrawable());
	}
}

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and here is MainActivity.java

package rs.limitline.topcider;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

	private Button button;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		button = (Button) findViewById(R.id.button1);
		button.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				Intent galerija = new Intent(
						"rs.limitline.topcider.GALERIJA_APARTMANI");
				startActivity(galerija);
			}
		});

	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}
}

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